Core assembly for an inductive device

ABSTRACT

A transformer of the shell type having two or more conductive coils physically in the form of closed loops and located side-byside along a common axis with magnetizable material being provided by a ribbon of grain-oriented steel spirally wound around the legs of the coils to embrace the latter. The magnetizable material may be provided by concentric cylinders of spirally wound ribbon steel with adjacent spirals having the ribbons located substantially perpendicular to one another. A cylinder with the ribbon perpendicular to the axis of the cylinder may be formed of a grain-oriented steel in which case the ribbon is undulated, facilitating bending the same into a close spiral. The undulations are located in internested relation reducing the likelihood of noise. The core and coil assembly is enclosed in a casing conforming substantially in shape to the outline configuration of the core and coil assembly and bushings are secured to the casing. Heat dissipation is facilitated by fins projecting outwardly from the casing and also by utilizing heat sinks having a portion located between the coils and a further portion projecting outwardly therefrom in direct physical contact with the casing. The heat sinks are preferably located so as not to intersect the high-density magnetic flux. The transformers may be constructed as identical units which may be stacked for increasing capacity and in which case the terminals are located electrically to interconnect adjacent units simultaneously with physically placing such units in stacked relation. A method of forming a coil is provided which includes simultaneously insulating the conductor turns one from the other and encapsulating the coil in a potting compound. To effect this, a spacer is applied to the conductor in the form of glass strands spirally wound onto the conductor and the conductor is thereafter wound into a closed loop coil. The formed coil is then placed in apparatus for impregnating the coil with an encapsulant. The same method is utilized to form a transformer with the encapsulation being effected with the core and coil assembly physically located within the transformer casing.

United States Patent [72] Inventors Anthony B. Trench 25 Elizabeth St., Thornhill; Vaughan 1. C. Marks, 56 Blakemanor Blvd., Scarborough; Wllllam T. Arnold, RR. #1, Queensvllle, all of Canada [21] Appl. No. 814,705 [22] Filed Apr. 9, 1969 [45] Patented Nov. 2, 1971 [32] Priority Apr. 11, 1968 [33] Canada [31] 017,329

[54] CORE ASSEMBLY FOR AN INDUCTIVE DEVICE 12 Claims, 22 Drawing Figs.

[52] US. Cl 336/61, 336/96,336/211, 336/212, 336/213, 336/218, 336/234 [51] Int. Cl ..H01127/08, H01f27/24 [50] Field olSearch 336/55,61, 96, 83,218,212, 21 l, 107, 233, 234,213

[56] References Cited UNITED STATES PATENTS 1,910,253 5/1933 Keinath 336/213 2,584,564 2/1952 Ellis 336/213 2,962,679 11/1960 Stratton. 336/212 X 3,146,420 8/1964 Knobel 336/212 1,602,043 10/1926 Pfiffner 336/96 X 1,680,910 8/1928 Pfift'ner 336/61 X 2,314,912 3/1943 Troy 336/83 X 2,401,984 6/1946 Steinmayer 336/212 X 2,770,785 11/1956 Haagens et al... 336/55 X 2,832,012 4/1958 Kleason et al. 336/61 X 3,195,081 7/1965 Kunes 336/218 X 3,210,701 10/1965 Fastner et a1. 336/96 3,223,954 12/1965 Mateer 336/107 X 3,252,118 5/1966 Hughes... 336/211 X 3,305,811 2/1967 Toombs............... 336/83 3,309,641 3/1967 Burkhardt et a1. 336/211 3,428,928 2/1969 Maines 336/61 3,464,041 8/1969 Waterman sacs/234x 3,467,929 9/1969 Derbyshire m1 336/61 7 FOREIGN PATENTS 356,947 1931 GreatBritain 336/213 Primary Examiner-Thomas J Kozma Attorney-Shanley and ONeil ABSTRACT: A transformer of the shell type having two or i more conductive coils physically in the form of closed loops and located side-by-side along a common axis with magnetizable material being provided by a ribbon ofgrain-oriented steel spirally wound around the legs of the coils to embrace the latter. The magnetizable material may be provided by concentric cylinders of spirally wound ribbon steel with adjacent spirals having the ribbons located substantially perpendicular to one another. A cylinder with the ribbon perpendicular to the axis of the cylinder may be formed of a grain-oriented steel in which case the ribbon is undulated, facilitating bending the same into a close spiral. The undulations are located in internested relation reducing the likelihood of noise. The core and coil assembly is enclosed in a casing conforming substantially in shape to the outline configuration of the core and coil assembly and bushings aresecured to the casing. Heat dissipation is facilitated by fins projecting outwardly from the casing and also by utilizing heat sinks having a portion located between the coils and a further portion projecting outwardly therefrom in direct physical contact with the casing. The heat sinks are preferably located so as not to intersect the high-density magnetic flux. The transformers may be constructed as identical units which may be stacked for increasing capacity and in which case the terminals are located electrically to interconnect adjacent units simultaneously with physically placing such units in stacked relation. A method of forming a coil is provided which includes simultaneously insulating the conductor turns one from the other and encapsulating the coil in a potting compound. To effect this, a spacer is appliedto the conductor in the form of glass strands spirally wound onto the conductor and the conductor is thereafter wound into a closed loop coil. The formed coil is then placed in apparatus for impregnating the coil with an encapsulant. The same method is utilized to form a transformer with the encapsulation being effected with the core and coil assembly physically located within the transformer casing.

SHEET 2 OF 6 PATENTED NUVZ l9?! PATENTEDuuvz nan 3517,9555

SHEET 3 BF 6 CORE ASSEMBLY FOR AN INDUCTIVE DEVICE This invention relates to electromagnetic induction apparatus.

Transformers, in general, are classed by the type of cooling and also by the type of core structure. Cooling may be effected by natural or forced circulation of a cooling fluid through suitable passages in the transformer assembly. Such construction requires a space between the casing and core and coil assembly. The fluid may be air, gas, an oil or a synthetic fluid. The most commonly known and used type of transformer is the core type. The other less popular type is referred to as a shell-type transformer. Disadvantages and drawbacks of such conventional transformers are discussed briefly in Canadian Pat. No. 728,298 issued Feb. 15, 1966. The present invention is concerned with a shell-type transformer and preferably within the range of 5 kva. to 100 kva. Transformers of this size are nonnally located outdoors in power distribution systems and they have been, for the most part, cooled by circulation of a cooling fluid through the assembly. This results in a unit of relatively large size and thus ultimately expensive to construct.

Shell-type transformers are well known as exemplified by Canadian Pat. Nos. 387,222 issued Mar. 5, 1940; 408,663 issuedNov. 1942; 421,786 issued Aug. 1, 1944; 420,193 issued May. 16, 1943; 387,223 issued Mar. 5, 1940; 438,207 issued Nov. 26, 1946; and $21,487 issued Feb. 7,1956.

The transformers illustrated in the above patents co'nsist generally of a coil and core assembly where the coil portion includes at least two coil elements in the physical form of closed loops and the core includes a ribbon of magnetizable material spirally wound around selected portions of the the closed loops. This type of transformer is sometimes referred to as a wound core transformer but more commonly is known as a shell core transformer. The magnetizable material is preferably a grain-oriented silicon steel with the grain-orientation substantially parallel to the length of the strips as is well known in the art. it has been a problem in the past to dissipate heat from shell core transformers which, accordingly, necessitated over-design for any given installation. The over-design accordingly has contributed to making then less acceptable thus placing them noncompetitive with the other more commonly used types of transformers.

Transformers of the foregoing general type are critical from a design consideration as is acknowledged by the above patentees. Losses in induction devices are due to a large extent from stray field losses, i.e. stray flux. These losses occur as hot spots in a transformer necessitating over-design of the coil conductors and/or magnetizable material. Stray fields (caused by stray flux) furthermore represent a loss in efficiency of the device because the stray flux is not contributing to linking the coils inductively.

Various proposals have been made for dissipating heat from transformers as exemplified by the following U.S. Pat. Nos. 3,243,744 issued Mar. 29, 1966 to A. A. Halacsy; 3,142,809 142,809 issued July 28, 1964 to T. Remenyik; 1,385,624 issued July 26, 1921 to A. A. Kent; 1,602,043 issued Oct. 5, 1926 to E. Pfiffner.

These proposals however failed to provide a simple device for use in dissipating heat and, at the same time, not interfere with assembling the device and/or the electrical and magnetic properties of the device.

The shell-type transformer, l.e. transformers of the foregoing type have been an attempt at improving the efficiency of transformers. An ideal transformer generally is considered one consisting of a toroidal coil and a toroidal device. in the past however, difficulties have been encountered in making a toroidal core and particularly using stacked layers of ribbon material. Because of the dimculties in forming the ribbon material into a core, the shell-type transformers of the foregoing type have the ribbon material wound flatwise about the longitudinal axis of the conductor. This requires having relatively straight leg portions in the coil and consequently is not of the ideal circular form.

date with one of larger size. There are also considerable manufacturing and storage problems in having to make transformers of many different sizes to meet the requirements. Accordingly, it is a principal object of the present invention to provide a transformer economical to construct and, at the same time, one which may be stacked along with similar units to vary the overall capacity.

A primary object of the present invention is to provide a transformer which is relatively small and cheap to construct compared to known transformers of equivalent capacity.

A further object of the present invention is to provide a transformer which is reliable through a relatively long life compared to the present distribution transformers.

A further object is to'provide a shell-type transformer which is more competitive with other known types of transformers than present shell core transformers.

A further object is to provide a transformer whichdoes not have cooling fluids circulated therethough.

A further object of the present invention is to provide an improved core for use in a transformer.

A further object of the present invention is to provide a core of ribbon material which may be used on a generally circular or toroidal coil.

A further object of the present invention is to provide a transformer shell core of ribbon material with the ribbon flat faces angularly disposed with respect to the longitudinal axis of the conductor.

A further object of the present invention is to provide an improved composite core for an induction device.

A further object of the present invention is to provide a spirally wound ribbon core edgewise disposed with respect to the length of the ribbon and having the grain orientation of the material extending in a direction parallel to the length of the ribbon. It is well known in the transformer art to have the grain oriented so as to be in a direction parallel to the length of the ribbon, such grain orientation however, provides little if any resistance to longitudinally directed shear stresses. This has not been a problem in the prior technique because of the spirally wound ribbon being wound flatwise about a longitudinally extending conductor.

A further object of the present invention is to provide a simple and efficient heat-dissipation device in a transformer of the core or shell type.

A further object of the present invention is to improve the efficiency of a core and coil assembly by converting at least a portion of what otherwise would be stray flux, to flux useful for inductively coupling the coils.

A further object of the present invention is to improve the dissipation of heat from coils and thereby improve the efficiency of an inductive device.

A further object of he present invention is to improve the efficiency of the coil and core assembly by at least partially reducing the hot spots and thereby reducing the amount of over-design as would otherwise be required.

A further object of the present invention is to provide a relatively large range of transformer sizes utilizing a minimum number of transformer units of different size.

A further object of the present invention is to minimize the steps involved to form an encapsulated coil consisting of a plurality of turns of conductor insulated one from another.

in accordance with one aspect of the present invention, there is provided a transformer comprising in combination a core and coil assembly having heat-dissipating means associated therewith comprising a casing disposed in compete surrounding relation with respect to the core and coil assembly and conforming substantially to the shape thereof, said casing consisting of a highly heat-conductive material and thereby providing a relatively large mass of heat-conductive material in surrounding relation with respect to the entire core and coil assembly for dissipating heat from the unit.

In accordance with a further aspect of the present invention, there is provided a transformer comprising at least two conductive circuits physically in the form of a closed loop and located side-by-side along a common axis, at least one body of magnetizable material circumscribing a common selected portion of said closed loops, a casing enclosing said conductive circuits and magnetizable material and a potting compound filling the space between the casing and the remainder of the assembly to provide a substantially solid transformer unit. By solid construction, or solid transformer, is meant that there are no passages or chambers in the transformer for the circulation of a cooling fluid therethrough.

In accordance with another aspect of the present invention, there is provided in the art of dissipating heat from core and coil assembly of an inductive device by strips of heat-conductive material extending outwardly from the coils of the device, the improvement comprising locating such conductive strips of material, in an AC device so as not to intersect the paths of the high-intensity flux.

In accordance with a further aspect of the present invention, there is provided in an AC inductive device having at least two conductive coils disposed side-by-side along a common axis and a magnetic circuit therefor including magnetizable material circumscribing a common portion of said conductive coils, the improvement comprising at least one strip of heat-conductive material disposed in a plane parallel to the path of the alternating stray flux field, said strip of material projecting outwardly from said coils and extending along a selected portion of the length thereof.

in accordance with another aspect of the present invention, there is provided in an inductive device including at least two coils and a magnetizable material circumscribing selected portions thereof, an improvement comprising collecting and redistributing stray magnetic flux.

In accordance with a further aspect of the present invention, there is provided in an inductive device having at least two conductive coils and a magnetic circuit comprising a main body of magnetizable material circumscribing at least selected portions of said coils, the improvement comprising a plurality of relatively narrow strips of magnetizable material disposed side-by-side in edgewise relation intermediate at least selected portions of said conductive coils and said main body of magnetizable material.

In accordance with further aspect of the present invention, there is provided an improvement as described in the foregoing paragraph where the narrow strips are of a magnetizable material circumscribing the conductive coils.

In accordance with still a further aspect of the present invention, there is provided core steel for an inductive device comprising in combination an inner cylinder and an outer cylinder each consisting of a wound ribbon of magnetizable material disposed about a common axis, the flat surfaces of the ribbon of the innermost and outermost cylinders being disposed, respectively, substantially transverse and parallel to the said common axis.

In accordance with a still further aspect of the present invention there is provided a core for an induction device comprising a ribbon of magnetizable material helically wound about a selected axis with the flat faces of such ribbon directed outwardly at a selected angle to such axis, said ribbon having a plurality of undulations angularly disposed with respect to the length of the ribbon and being of grain-oriented material with the orientation extending in a direction substantially parallel to the length of the ribbon.

In accordance with another aspect of the present invention, there is provided a core for a transformer comprising a ribbon of magnetizable material having a plurality of undulations angularly disposed with respect to the length thereof and helically wound about a selected axis, the surfaces of such ribbon being angularly disposed with respect to said axis and extending in a direction outwardly therefrom.

In accordance with still further aspect of the present invention, there is provided a transformer comprising a pair of annular coil elements substantially completely circumscribed by a core of magnetizable material, said core comprising a ribbon helically wound about said coil and having the surfaces of the ribbon directed in a direction outwardly from such coils, said ribbon having a plurality of undulations angularly disposed with respect to the length thereof.

In accordance with a further aspect of the present invention, there is provided a method of forming a cylinder from an edgewise disposed ribbon of grain-oriented material wherein the grain is generally parallel to the length of the ribbon comprising crimping the ribbon at an angle to the length thereof to provide a series of undulations and spirally winding said ribbon into a cylinder of selected diameter having the flat faces of the ribbon at a selected angle with respect to the axis of said cylinder.

in accordance with a still further aspect of the present invention, there is provided a core of magnetizable material for an inductive device comprising in combination an inner layer and an outer layer each consisting of a ribbon of magnetizable material disposedabout a common axis, the surfaces of the ribbons of the innermost and outermost layers being disposed, respectively, substantially transverse to and coaxial with the said common axis, the ribbon of the innermost layer being crimped angularly of the length thereof. Preferably, the crimping extends substantially radially outwardly from the abovementioned common axis.

In accordance with a still further aspect of the present invention, there is provided a method of making a transformer comprising securing a spacer to a conductor and winding such conductor with a spacer thereon into a coil, enclosing such wound coil in a casing and filling the voids within such casing with a potting compound electrically to insulate the conductors one from the other and encapsulate the core and coil assembly to provide a solid transformer. ln the preferred form, the spacer on the conductor comprises an electrically insula tive material spirally wound around the conductor.

In accordance with another aspect of the present invention, there is provided a method of forming an encapsulated coil from a conductor comprising applying a spacer to said conductor, winding said conductor with the spacers thereon into a coil consisting of a plurality of turns retained in selected spaced relationship by said spacer elements, and impregnating said coil with a potting compound of electrical insulative material to insulate the conductors one from the other and simultaneously encapsulate the entire coil.

In accordance with another aspect of the present invention, there is provide a transformer comprising a casing enclosing a core and coil assembly, terminals for said coil terminating, respectively, on opposed faces of the casing, means for physically interconnecting two or more such transformers in stacked relationship and means electrically interconnecting said transformer simultaneously with stacking thereof.

In accordance with one aspect of the present invention, there is provided a transformer comprising in combination a core and coil assembly having heat-dissipating means associated therewith comprising a casing disposed in complete surrounding relation with respect to the core and coil assembly and conforming substantially to the shape thereof, said casing consisting of a highly heat-conductive material and thereby providing a relatively large mass of heat'conductive material in surrounding relation with respect to the entire core and coil assembly, and including a potting compound filling the space between the casing and the remainder of the assembly to provide a substantially solid transformer unit.

In accordance with another aspect of the present invention, there is provided a transformer as described in the preceding paragraph, including further heat-dissipating means comprising conductive strips of material so located as not to intersect the paths of the high-intensity flux. In the preferred form, the heat-conductive strips are in intimate contact with the casing and extend therefrom to selected positions between the highand low-voltage coils of the transformer.

In a more restricted aspect, there is provided a transformer of the foregoing type, including means to collect and redistribute stray magnetic fiux, said means in the preferred form, comprising a plurality of relatively narrow strips of magnetizable material disposed side-by-side in edgewise relation intermediate at least selected portions of the conductive coils and the main body of magnetizable material. If desired, the narrow strips are of a magnetizable material and circumscribe the conductive coils in which case they may be provided by a ribbon of magnetizable material spirally wound about a selected axis with the flat faces of such ribbon directed outwardly at a selected angle to such axis. The ribbon preferablyconsists of a selectively grain-oriented material in which case said ribbon includes a plurality of undulations angularly disposed with respect to the length of the ribbon with the grain-oriented to extend in a direction substantially parallel to the length of the ribbon. In the accompanying drawings,

FIG. 1 is a front elevational view of an electrical transformer;

FIG. 2 is a partial cross-sectional view taken substantially along section 2--2 ofFIG. 1;

FIG. 3 is a sectional view taken substantially along section 3-3 of FIG. 2;

FIG. 4 is an oblique view of a modified transformer;

FIG. 5 is a partial sectional view illustrating, an upper terminal bushing of the transformer illustrated in FIG. 4;

FIG. 6 is a cross section taken through the core and coil portion of transformer and illustrates a modified core assembly;

FIG. 7 is a cross section taken along section 7-7 of FIG. 6

FIG. 8 is a cross section similar to FIG. 6 illustrating modifications to the core shown therein;

FIG. 9 is a partial sectional view, similar to FIG. 6, diagrammatically illustrating the flux paths in the core and coil assem bly;

FIG. 10 is an oblique view illustrating a modification to a portion of the core illustrated in FIGS. 6 and 7;

FIG. 11 is a plan view of the core and coil assembly removed from the casing and including heat dissipating fins at selected locations;

FIG. 12 is a cross-sectional view taken substantially along section 12-12 of FIG. 11;

FIG. 13 is a plan view of a single heat dissipating fin;

FIG. 14 is a cross-sectional view similar to FIG. 12 but including the transformer casing, a modified coil portion, and multiple heating fins disposed in stacked relation;

FIG. I5 is similar to FIG. 14, illustrating a further modification to the heating fins;

FIG. 16 is a view similar to FIG. 11, illustrating a still further modification to the heat dissipating means in accordance with the present invention;

FIG. 17 is an enlarged partial sectional view of one corner of the coil and core assembly illustrated in FIG. 9;

FIG. [8 is a cross section of a coil similar to that illustrated in FIGS. 9 and 14 and diagrammatically illustrates various positions for the heat dissipating fins relative to the highand low-voltage coils;

FIG. 19 is a side elevational view illustrating a plurality of transformers interconnected;

FIG. 20 is a diagrammatic illustration of a process for making a coil assembly;

FIG. 21 is an oblique view diagrammatically illustrating winding ribbon core material on a closed loop coil; and

FIG. 22 is a diagrammatic illustration of apparatus used to encapsulate a coil, or a coil and core assembly.

Referring now in detail to the drawings, there is illustrated a transformer 10 consisting of a coil and core assembly 30 enclosed in a casing 50. The coil and core assembly 30 consists of induction coils 31 in the physical form of a closed rectangular loop and a core portion 32 embracing selected legs of the closed loop.

The induction coils 31 consist of a primary winding 33 and a secondary winding 34 (respectively, the low-voltage and highvoltage windings) connected by leads to bushings or terminal posts suitably located on the transformer casing. In the embodiment illustrated in FIG. 1, the posts are located within the perimeter of the coils but obviously they may be located. elsewhere, for example, at the outer corners (see FIGS. 4 and 5) if desired. Referring to FIGS. 1 to 3, the primary winding 32 is connected by respective leads 35 and 36 to terminal posts 37 and 38 and the secondary winding is connected by leads 39 and 40 to respective terminal posts 41 and 42.

Tile primary and secondary windings, as previously mentioned, are closed loops and may be wound simultaneously but preferably, they are wound individually and in the case of a single primary and a single secondary, they are each preferably semicircular in cross section as illustrated in FIG. 2.

The induction coils 31 are preferably rectangular, as illustrated in FIG. 3, consisting of substantially straight leg portions 43, 44, 45 and 46 each embraced by a core portion 32 of magnetizable material. Each of the core portions 32 consists preferably of a ribbon of steel spirally wound around the induction coils. Spirally wound magnetic material for transformers is well known as exemplified by the aforementioned Canadian patents as is also the method of applying the ribbon or strip material to the coils. The ribbon or strip may be of any well-known material, possessing good magnetic properties, e.g. silicon steel, and in order to facilitate applying the ribbon of material it may be annealed to provide a permanent set as is disclosed in the aforementioned Canadian Pat. No. 408,663. The method of winding the ribbon of material and apparatus for doing the same is disclosed in the aforementioned Canadian Pat. NO. 387,222. It is preferred that the grain orientation of the material in the ribbon be in the direction of the length of the strip as taught in the above-mentioned CanadianPat. No. 387,222 and, in order to provide a good space factor, the spirally wound layers of ribbon may be stepped with the ribbon on adjacent legs overlapping in a manner as taught in the aforementioned Canadian Pat. No. 421,786.

A modified coil portion is illustrated in FIGS 6, 9, 14, 15, 17 and 19 which consists of a central, substantially rectangular in cross section, low-voltage winding 200 disposed intermediate a pair of substantially semicircular, in cross section, secondary coil members 201. The primary winding 200 terminates in a pair of opposed flat faces 202 and 203 disposed respectively adjacent to a flat face 204 of respective ones of the pair of outer secondary windings 201. In this embodiment, there is a pair of heat sink members 500 at each of the four corners of the closed loop coil.

The casing 50 is a body of highly heat-conductive material conforming closely to the shape of the core and coil assembly. The conformed shape of the casing and coil and core assembly effectively provides a large mass of heat-conductive material on the external surface of the core and coil assembly and thus is capable of dissipating large quantities of heat. TI-Ie casing may be constructed in any convenient manner. In the embodiment illustrated in FIGS. 1 to 3, it consists of two identical sections 51 secured together as by rivets, bolts, welding or the like. The casing portion 51 has an outer annular grooved portion 52 terminating at the outer periphery in an outwardly directed flange 53 and at the inner edge in a reversely curved flange 54. The flange 54 terminates in an enlarged outer circular rim 55 having an annular groove 56 receiving a gasket for the purpose as will be seen hereinafter.

The casing preferably is made of aluminum or an aluminum alloy or the like material which is highly heat conductive and to further facilitate the dissipation of heat, the outer portion of the casing may include a plurality of outwardly directed ribs or fins 57. Similarly, a plurality of ribs 58 may, if desired, project inwardly toward the interior of the casing to engage the core portion of the coil and core assembly. In such case the internal ribs 58 retain the coil and core assembly in selected spaced relationship with respect to the interior of casing providing a chamber 70 to receive a potting compound or filling material to be described in more detail hereinafter. In the preferred form, however, there are no ribs on the internal surface of the casing but instead, such surfaces are relatively smooth conforming to the shape of the coil and core assembly. The interior dimensions and shape of the casing and the exterior dimensions of the cores are interrelated such that when assembled, the casing is in pressural engagement with the core steel 32. This facilitates the dissipation of heat.

In order to assemble the unit, the coil and core assembly may be placed in one-half of the casing and the other half then brought into mating relationship therewith. A jig or clamp assembly may be suitably provided to engage the ribs 53 and 54 bringing the same together (providing, if desired, pressural engagement of the casing and the core) and such ribs thereafter may be joined by welding, riveting or the like. After the unit has been assembled, the interior of the casing may be filled with a suitable potting compound. This can be effected by drawing a vacuum on the chamber such as by placing the assembled unit in a vacuum chamber and connecting a supply of fluid potting compound to the interior of the casing (for example, by a conduit) and having the fluid at a positive pressure with respect to the vacuum chamber. Bleeder conduits may be suitably connected to the chamber of the casing to be filled.

The potting compound may be a resin such as an epoxy, polyester or silicone type either filled or unfilled, or any other well-known types selected to provide suitable characteristics such as temperature of operation and thereby class the transformer as to operation. A high-temperature potting compound minimizes heat sinking and an epoxy found suitable is No. 2258 Epoxy of Union Carbide with CIBAI 972 hardener. Anhydride epoxy systems are deemed suitable. Numerous proposals have been made concerning various suitable encapsulants and in this regard, attention is directed to Canadian Pat. Nos. 761,60l and 734,998 issued, respectively, June 20, 1967 and May 24,1966.

The potting compound, alternatively, may be injected under pressure and in which event external ribs 57 suitably reinforce the casing to withstand the pressure while maintaining the casing in pressural engagement with the core portion 32. The resin is then cured and this may be done while the transformer is in the vacuum chamber or while it is outside of the vacuum chamber or a combination of both. This may be effected at least in part by energizing the coils of the transformer sufficiently to provide heat when using a thermal setting resin. This causes curing from the inside out minimizing voids, the latter of which are undesirable.

The leads from the primary and secondary windings may be brought, as previously suggested, though the casing at any suitable location, for example, either the interior or the exterior of the generally rectangularly shaped coil assembly. Suitable apertures in the casing may be provided such that the leads can be brought to the exterior of the casing by bushings or the like so as to facilitate connecting the same to an electrical circuit. The apertures may be provided, for example, by aligned enlargements in adjacent surfaces of the transformer casing portions 51. In the embodiment illustrated in FIGS. 1 to 3, the leads 35, 36, 39 and 40 extend through aligned enlargements 59 in the adjacent abutting surfaces of flanges 54. As illustrated in FIG. 2, the leads are connected to terminal members located in an enclosed chamber 80 defined by a spaced pair of plates 81 secured to respective ones of the casing sections 51. Each plate 81 is a disclike member, which may be secured as by welding or the like, to the flange 54 of the casing, or alternatively, the enlarged ribbed portion 55 may be utilized to ensure that the disc cannot be removed from an assembled transformer.

A plurality of insulated bushings 83 are secured to each of the plates to provide a mounting for the terminals 37, 38, 41 and 42. Each bushing 83 may be ceramic some other insulative material having an outer portion 84 and an inner portion 85 connected together by a restricted neck portion 86. The restricted neck 86, in effect, defines a peripheral groove for receiving a portion of the wall and thereby retains the bushing in position. The neck portion 86 passes through an aperture in the wall or plate 81 and where the bushing is made of a rigid or semirigid material the inner portion 85 may be a nut threaded onto a portion of the neck or stem 86 which projects through the aperture in the disc.

The bushing includes a central aperture 87 and in the embodiment illustrated in FIGS. 1 and 2, the terminals on one side of the transformer are female portions of a coupling and the terminals on the other side are male portions of coupling members. The female coupling portion is provided by a brass or other conductive sleeve member 89 inserted into the aperture 88 of the bushing. A pin 90 is connected to the sleeve 89 as by brazing, welding, pressural engagement or the like and projects through the bushing in the other plate. The pin terminates in an end portion 91 having a diameter of such size as to fit snugly into the brass sleeve 89 of an adjacent transformer unit. The projecting terminal end pin portions 91, on one side of the transformer, are in alignment with respective ones of the sleeves in the bushings on the other side whereby two or more transformer units may be electrically connected simultaneously with being brought into side-by-side engagement, i.e. stacked relation.

Alternatively, the bushing may pass through enlargement in the casing outer flanges 53. For example, as shown in FIG. 4, the low-voltage leads 37 and 38 are connected to terminals of respective bushings 37A and 38A projecting downwardly from the casing adjacent respective opposite corners of the transformer and similarly, the high-voltage leads 39 and 40 are connected to terminals of respective bushings 41A and 42A projecting upwardly from the transformer. Details of the terminal posts are illustrated in FIG. 5 and will be described hereinafter.

A gasket 100, of any suitable sealing material, in the form of an O-ring may be inserted in the groove 56 of one unit and be of such dimension as to project into the groove 56 of an adjacent unit and thereby provide a sealed, enclosed area for the terminals of the interconnected transformer units.

Each transformer casing includes an enlarged portion of the flange 53 at each of the four corners of the rectangularlyshaped unit and each such portion may, if desired, include an aperture 60. A rod or similar element may be inserted through aligned apertures 60 in adjacent transformer units connected together to retain the same in interconnected relationship when stacked for increasing the capacity of the transformer.

FIG. 19 illustrates three transformer units 10 interconnected by a plurality of rods having threaded portions passing through each of the transformer casing apertures 60 and a pair of lock nuts 101 are located on one each side of each transformer casing thereby providing a rigid assembly of interconnected transformers disposed side-by-side in stacked relationship. Each transformer unit may, for example, have a capacity of 5 to 100 kva. In the event a capacity of 75 kva. is required, three 25 kva. units may be stacked side-by-side.

In the embodiment illustrated in FIG. 19, the terminal rib 55 of the casing is located substantially outwardly of the remainder of the casing so as to provide a relatively large space between adjacent transformer units. The space between the unit provides a channel or column facilitating the circulation of air around the individual units and thus facilitates the dissipation of heat from each of the individual transformer units.

The transformer illustrated in FIGS. 1 to 3 is of the dry type and the casing conforms substantially to the shape of the core and coil assembly. Illustrated in FIGS. 4 and 5 is a modified transformer 10A consisting of a casing 50A having a plurality of outwardly directed ribs 57A. The ribs 57A, on the two vertically disposed legs, extend parallel to the leg while the ribs on the outer two legs circumscribe the same and are directed radially outwardly therefrom transverse to the longitudinal axis of such legs. As previously mentioned, the terminal bushings 37A, 38A, 41A and 42A are located at the corners of the rectangular assembly and referring to FIG. 5, there is illustrated in detail the construction of bushing 41A. Referring now to this figure, the bushing consists of a post P projecting through an aperture A in the sidewall of the transformer casing 50A. The aperture A has a tapered wall directed inwardly toward the interior of the casing chamber which receives the core and coil assembly and corresponds in shape to an enlarged lower terminal end P1 of the post. The shape of the aperture and the terminal end of the post serve to prevent the post from being removed from the casing. The post P is of an insulated material which, for example, may be a cast resin, a ceramic material or the like, and includes a ferrule F embedded therein. The ferrule has a recess in one end thereof to receive a terminal end C of a conductor of one of the coils and the opposite end has a threaded bore B for receiving a threaded end portion of a terminal post TP. The post P has a conical recess R in the outer end thereof which tapers downwardly and inwardly terminating in a lower end portion substantially flush with the end of the ferrule having the threaded bore 8 extending therefrom. An insulated bushing member is clampingly held against the post P by a locknut N1 threaded onto the terminal post TP and bears against the outer end of member CB. The opposite end of member CB corresponds in shape to the conical recess R and the sloped sidewalls are preferably in tight pressural engagement preventing entry of foreign matter into the connection of the terminal post to the ferrule. The connectors accordinglyare protected from the elements and, if desired, suitable sealing materials may be utilized completely separating the connections from the air and thus avoiding deterioration which might otherwise be caused.

The terminal post TP has a threaded outer end having a further nut N1 threaded thereon and which serves to connect the conductor of an external circuit to the terminal post.

The transformer illustrated in FIGS. 4 and 5 may be a solid type wherein the core and coil assembly is encapsulated in a potting compound in which case the post P may be a post formed in the encapsulant material in which case the coil terminal end conductor C and the ferrule to which it is connected are completely encapsulated and protected from the atmosphere.

In each of the foregoing embodiments of the dry transformer, the casing conforms in shape to that of the core and coil assembly and thus provides a relatively large mass of highly heat-conductive material completely surrounding the core and coil assembly. This facilitates the dissipation of heat while, at the same time, providing a relatively rugged assembly. The transformer of the foregoing type may be mounted on a post above ground as is normally done in power distribution systems or alternatively, it is suitable, because of its dry and solid construction, to be buried underground.

The cores 32, as previously mentioned, consist of ribbon magnetizable material wound around the various leg portions of the rectangular-shaped coil. The core 32 illustrated in FIG. 3 is directly wound onto the various leg portions and is preferably in tight intimate contact with the coil. A modified core assembly is illustrated in FIGS. 6 to 9 inclusive. Referring to FIG. 6, the core portion or unit 32 for the transformer consists of an outer layer 300 of magnetizable material circumscribing a second or inner layer 301 of similar material. Each layer 300 and 301 preferably consists of a wound ribbon of material which is preferably grain oriented with the grain running in a direction substantially parallel to the length of the ribbon. The individual ribbons in the outer layer 300 and the individual ribbons in the inner layer 301 are disposed substantially at right angles to one another. The ribbon in the layer 301 is in effect helically ribbon material in cylindrical form with its faces perpendicular to the axis of the cylinder and the outermost layer 300 has its faces cylindrically disposed about the same axis.

The ribbon material in layer 301 is edgewise disposed with respect to the coil 200 which passes through the central opening of the layer. The ribbon is preferably in contact with the coil and because of the ribbon being edgewise disposed with respect thereto, the layer acts as a series of fins facilitating dissipation of heat from the coil.

A further function of the layer 301 is to collect stray or cross flux. In FIGS. 6, 9, and 14 to 17, there is diagrammatically illustrated a coil 30 consisting of a central primary winding 200 located intermediate a pair of secondary windings 201. The primary winding 200 is generally rectangular in cross section having a pair of opposed chordal flat faces 202 and 203 in faceto-face relation with respective ones of a flat face 204 on the respective ones of adjacent secondary coils 201. In FIGS. 2 and 12, the coil consists of windings 33 and 34 each semicircular in cross section. In a transformer of the type illustrated, there is a concentration of flux entering and leaving at the junction of the primary and secondary coils. This concentration of flux is illustrated diagrammatically in FIG. 9 by the arrows at each of the four corners of the coil primary winding 200, these being identified by the letters J. K, L and M. At the corners J and L, the flux is emerging from the induction coils and at the corners K and M, the flux is entering. In either event the flux is generally in a direction transverse to the flat surface of the ribbon of material in the outer spiral winding 300. The edgewise disposition of the ribbon in the layer 301 facilitates entry of the flux. At the corners J and L, the cross flux, or stray flux as it may be referred to, is collected by ribbons and because of the ease with which it enters the edgewise disposed ribbons compared to one flatwise there is a reduction in the heat of an otherwise hot spot. Also, the collected flux is redistributed and usefully employed to inductively couple the coils by being directed in a direction circumscribing the coils.

An alternative embodiment of the core portion 301 of the coil core assembly, is illustrated in FIG. 8 wherein the cylindrical body of ribbon material 301 is replaced by a pair of segmental units 310 and 320 each consisting of a series of flat elements of a magnetizable material disposed side-byside. In effect, each assembly 310 and 320 is a segmental portion of the cylindrical spiral of ribbon 30] illustrated in FIG. 6.

In the embodiment illustrated in FIG. 6, there would be, in effect, two parallel flux paths circumscribing the conductors of coil 30, one flux path through the ribbon 301 and the other located outwardly therefrom in the ribbon 300. The ribbon 300, of course, is the main body of the magnetic circuit for the transformer unit and the ribbon 301 may be considered a secondary body. In such an arrangement, however, the magnetic circuits are parallel while in FIG. 8 the arrangement is generally of a parallel-series combination.

In the arrangement in FIG. 8, the segmental units 310 and 320 are positioned at the points of flux concentration, i.e. the comers J, K L andM for collecting the cross flux and transferring such flux into the primary magnetic circuit or outer ribbon 300. The arrangement accordingly provides parallel paths for the flux adjacent the upper and lower flat sides of the coil conductor while at each of the two positions at right angles thereto, the two flux paths are, in effect, in series. Such an arrangement is not as efficient as where the ribbon 301 circumscribes the coil conductor as in FIG. 7, but on the other hand, it permits using various cross-sectional shapes of the coil con ductor, for example, in FIG. 8 the primary winding is substantially square in cross section whereas the secondary windings are each semicircular. If desired, all of the coil windings could be rectangular or square in cross section with the segmental units 310 and 320 appropriately shaped as to fill the entire space between the conductor coils and the magnetizable material which provides the main magnetic circuit, i.e. the ribbon of material 300 circumscribing the coil conductor. It will also be apparent that the suitably-shaped units may be positioned at only the corners J and I. here the flux is emerging from the coil conductor. The flux which is escaping will thus be readily collected and used by being directed in paths cir cumscribing the coil conductor.

The points which have been indicated as J, K, L and M in FIG. 9 are, in effect hot spots in instances where the edgewise disposed steel 301-310-320 is not used. In the case of using the edgewise disposed steel these hot spots are substantially reduced in temperature if not eliminated because of the greater ease with which the flux enters the steel by way of many edges rather than through the flat surface in a cases where the steel is wound directly onto the coil conductor as illustrated in FIGS. 2 and 3.

The layer 301 shown in FIGS. 6 and 7 may be termed a slinky steel core because it has the appearance of the wellknown slinky toy on the market. In the preferred form, the flat surfaces of the ribbon are substantially perpendicular to the axis of the longitudinal conductors in the coils i.e. perpendicular to the length of coil leg 43 or 44 etc. However, as previously mentioned, it may alternatively be angularly disposed with respect thereto.

As previously mentioned, it is preferable from a magnetic point of view, to have the grain orientation of the magnetizable material parallel to the length of the ribbon. Steel or silicon steel, which is normally used as the magnetizable material, is extremely brittle with such grain orientation and splits longitudinally when the steel is bent in a direction transverse to the length of the strip and in the plane of the flat face of the strip. In order to form the flat ribbon of brittle material into a spiral of cylindrical form where the flat faces of the ribbon are perpendicular to the axis of the ribbon, it is necessary to provide undulations in the strip. Soft ductile materials need not be deformed but such materials are normally unsuitable for transformer cores.

Referring to FIG. 10, there is illustrated a cylinder 400 made from a ribbon 401 of magnetizable material wound about an axis 402. Only two helical turns of ribbon are illustrated; however, it is understood that there are as many such turns as are required to form an appropriate length of cylinder. In the embodiment illustrated, the grain is parallel to the length of the ribbon and in order to facilitate the bending of the ribbon into the spiral, the ribbon is corrugated to provide a series of alternate valleys and crests 403 and 404 disposed in internested relationship in adjacent turns of the ribbon. The valleys and crests 403 and 404 each terminate in a ridge preferably directed radially outwardly from the central axis 402 and are preferably formed before annealing the strip of core material. If desired, the cylindrical form maybe accomplished by interrelating the depths of crimping at respectively the inner radius RI and the outer radius R2 in which case the depth of the crimp at R1 will be somewhat greater than the depth at R2. Alternatively, the ribbon may be crimped at a selected angle to its length and thereafter wound into a cylinder of selected diameter. In the latter instance, the crimping provides selected areas of definition which, during winding the ribbon into a spiral, confines further bending to those areas. In other words, the crimping is further modified in amplitude at either the inner diameter R1 or outer diameter R2 or both during winding the ribbon into the spiral. In either event the circumferential length of the edges of the ribbon at the inner and outer respective radii RI and R2 are substantially the same because the apparent difference is absorbed in the crimping. The bending of the ribbon to forma cylinder may be accomplished accordingly without damage to the ribbon as there is little or no shear stress during bending.

The alternate crests and valleys also provide a stiffening of the ribbon and should any portion of the ribbon be loose in an assembled transformer there is less likelihood of vibration and thus a reduction in noise in operation. Furthermore, the internested relationship has a tendency to interlock the adjacent ribbons preventing vibratory movement common to looseleaf material in an induction device.

The core may be used as the only core portion of an induction device in which case it may be readily formed into a toroidal shape by bending the cylindrical core into an arcuate path conforming to the curvature of the annular coil. The undulations in the ribbon permit utilizing a ribbon of most any width and in the preferred form, the undulations in adjacent helices are internested. The ribbon is effectively edgewise disposed with respect to the length of the conductor and thereby provides a radial heat path flow facilitating heat. It will also be appreciated that crinkling of the ribbon causes the ribbon to have the same flux path length adjacent the conductor as it does remote from the conductor. As previously mentioned, the core is effectively a Slinky and because of being edgewise disposed, it can extend substantially the entire length around an annular coil.

As previously mentioned, the casings 50 and 50A are provided with external fins to facilitate dissipating heat from the transformer. Each transformer may be provided with further means, generally referred to herein as heat sinks to facilitate the dissipation of heat. Accordingly, each transformer may have only external fins on the casing, or heat sinks (to be described hereinafter), or a combination of both to facilitate dissipating heat.

Referring to FIG. 11, the core and coil assembly 30 is illustrated without reference to the external casing (50 or 50A as the case may be) and included in such assembly are heat sinks 500 located at each of the four corners of the rectangular coil 31. Each heat sink 500 is a flat planar strip or plate of highly heat-conductive material such as copper; aluminum, or the like and is generally L-shaped having leg 501 and a leg 502 disposed substantially at right angles to one another. The legs 501 and 502 are preferably formed as a single plate; however, they may be independent of one another such that each heat sink consists of two individual parts meeting, for example, along a line 503 as indicated in phantom in FIG. 13. In an assembled structure, the respective legs 50] and 502 are interposted between the adjacent faces of the primary and secondary coils (which in the FIGS. 2 and i2 embodiment are respectively coils 33 and 34) with the legs 50] and 502 projecting into the central opening of the respective adjacently disposed core members 32. The legs 501 and 502 terminate at the opposite end in respective fin or leg portions 504 and 505 each of which may include, if desired, an aperture 506, the purpose of which will become apparent hereinafter. The coil members 33 and 34 are disposed side-by-side along a common axis and the fins 504 and 505 have their flat planar surfaces at an angle (preferably to such axis. The legs 501 and 502 pick up heat from the centralportion of the core members 32 as well as from between the adjacent coils 33 and 34 and conduct such heat outwardly facilitating cooling the entire induction device.

In the foregoing description, the heat sinks are described as being physically located between the adjacent coils. It will be realized that this physical location places the planar strips of heat-conductive material (the heat sinks) in planes parallel to the path of the high-intensity flux. Accordingly, the heat sinks do not interfere with he magnetic properties (and ultimately the electrical properties of the transformer). This is more clearly illustrated in FIG. 18. Tl-Ie high-intensity flux consists of the leadage flux which is indicated by arrows O, P and W. The arrows O and W indicate the flux paths respectively in he pair of outer secondary coils 201 and arrows P indicate the high-intensity flux path in the primary coil 202. There is a plane between the flux paths where the members 500 may be located such that the flux has little or no effect on the member and for convenience of description such plane is referred to herein as the flux neutral plane. The planar strips are located in these flux planes. Further heat sinks, which consist of arcuate strips, may also be positioned adjacent the outer surfaces of the coil. A pair of such further strips (500A) are diagrammatically illustrated adjacent respective opposed arcuate surfaces of the primary coil 202. Similarly, a pair of arcuate strips 5008 may be located adjacent respective outer surfaces of the secondary coils 201. The arcuate portion of the strips 500A and 5008 are positioned such that their marginal edges are set back from he junction of the primary and secondary coils Such arcuate portion is located between the coil and the core of the core and coil assembly and the remainder of the fin extending beyond the core may be bent in another plane directed outwardly from the coil. in such instance, the heat gathering portion only of the heat sink is located in a plane parallel to the path of the high-intensity flux. The remaining portion, however, is remote from he field of the flux. Effectively, the fins are disposed in such orientation that they do not intersect a strong magnetic field.

As previously mentioned, the coil may consist of a primary 33 and secondary 34 (FIG. 2) or a primary 200 and a pair of secondaries 201. In either of the embodiments, the finned portions 504 and 505 of the heat sinks 500 project outwardly from the coils and preferably to such an extent they engage the casing. As illustrated in FIG. 14 the heat sinks 500 are clampingly engaged between peripheral flanges 53 of the mating casing portions 51. In the case of the embodiment illustrated in FIG. 12, the fins 504 and 505 are in direct contact with each of the adjacently disposed flanges 53 whereas in FIG. 14, an insert 510 is interposed between he pair of heat sinks 500. Insert 510 may include a pair of apertures aligned with he apertures 506 in each of the heat sinks 500 and a pin 51] may be used to retain the casing segments 51, the insert 510, and the pair of heat sinks 500 in an assembled relationship and in tight pressural engagement. The tight pressural engagement not only facilitates the transfer of heat but it ensures also that the interior of the casing will be sealed from the ex terior elements such as rain, dust and the like. It is, of course, obvious that the rivets 511 may be replaced by welding the entire assembly so as to form a tight enclosure for the coil and steel assembly and also provide intimate contact between the heat sinks and the transformer casing.

Referring to FIGS. 16 and 17, there is illustrated a modified heat sink 600 located at each of the four corners of the rectangular coil conductor 31 having flat leaf material spirally wound on each of the four legs to provide core portions 32. The coil assembly 31 consists of a central primary winding 200 and a pair of outer secondary windings 201 previously described.

The heat sinks 600 consist of an inner body portion 601 and an outer cap 602 secured together, for example by joining outwardly directed flanges 603 and 604 located respectively on body members 601 and 602. The inner member 601 consists of a half segment of a cylinder bent at right angles to terminate in respective opposed ends 605 and 606. The outer cap 602 is similarly formed terminating respectively in opposed end faces 607 and 608 located substantially in the same plane as respective end faces 605 and 606 of the inner body members 601. The inner member and outer cap, respectively 601 and 602, together form a substantially cylindrical member having an outer wall 609 and an inner wall 610. Secured to the inner wall 610 of the body portion 601 is a pair of flat planar metal angle members 620 and 621 disposed in selected spaced rela tionship corresponding to the opposed faces 202 and 203 of the winding 200 and the adjacent flat face 204 of respective ones of the outer pair of coils 201. Each plate or angle member 620 and 621 includes a leg 622 and a leg 623 disposed at right angles to one another and having the fat surfaces of such legs in a common plane.

The assembly of the body member 601 and the angle members 620 and 621 may be part of a winding form for use in winding the coils 200 and 201. The body 601 of each of the four heat sink units 600 illustrated in FIG. 9 may be suitable secured to a jig and conductors wound simultaneously to form individual coils 200 and 201. The cross-sectional shape of the coils obviously will be determined by the space between the adjacent members 620 and 621 an the opposite face of such members together with the respective adjacent inner wall 610.

The outer cap 602 may, if desired, have a pair of longitudinal grooves 625 and 626 to receive an outer edge portion of respective ones of the members 620 and 621 at the junction of respective legs 622 and 623. The cap 602 preferably is in pressural contact with the respective members 620 and 621 facilitating the transfer of heat from the members to the cap.

As illustrated in FIG. 17, the legs 622 and 623 project inwardly toward the center of the adjacent steel members 32 and thereby act as heat conductors to dissipate the heat from the central portion of the core assembly. The members 622 and 623 are also located between the coils and thus facilitate dissipating heat from the internal portion of the coil assembly.

The heat sinks which are fins or flat plates are disposed at selected spaced intervals around the axis of the coils. The fin could, if desired; be substantially an annular element interrupted by a slot or gap. A complete annular element would constitute a short circuit turn which would be undesirable. They may be aluminum, copper of the like and may be a single thickness or laminated, the latter being desirable from the point of view of minimizing eddy-current losses.

in FIG. 20 there is illustrated schematically a method of forming a coil suitable for induction devices, for example a transformer. Referring in detail to FIG. 20, a wire conductor 700 is drawn off a spool 701 pivotally mounted on a shaft 702 by a driven winding mandrel 703. The wire may be either a bare wire or an insulated wire and in either event, an adhesive material 705 is applied (or formed) on at least selected portions of the conductor for holding the spacer on the conductor as will become apparent hereinafter. The adhesive material, when applied to the conductor, may be applied either as a continuous film or alternatively, strips extending longitudinally of the wire. In FIG. 20, the wire is illustrated as being drawn through adhesive material 705 contained within a tank 706 and, in the preferred form is a silicone adhesive. With regards to applying the adhesive to the conductor, the bath-type procedure illustrated in FIG. 20 may be replaced by rollers,

brushes or the like applicators. In the case of an insulated conductor, the coating on the conductor which provides the insulation may be suitably treated as, for example, by the application of heat or a solvent to provide a tacky outer surface.

Downstream from the adhesive-applying station, the wire with the adhesive thereon is indicated in FIG. 20 generally by the reference numeral 715. Downstream of the adhesive coated conductor 715, filament glass 710, in rope form, is drawn off a bobbin 711 mounted on a shaft 712 to rotate about a substantially horizontal axis and applied to the conductor. The rope form of filament glass is drawn off the bobbin 711 by a winding arm 713 mounted to rotate about the axis of the conductor. The winding arm consists of a member directed outwardly from the axis and has at least one arm adjacent the free end thereof extending parallel to the length of the conductor. The filament glass is drawn off the bobbin through a combing element 714 to form the strands into a flat ribbon and such flat ribbon is spirally wound around the conductor by the winding arm as the wire is moved horizontally to the right in Fig. 20. Adjacent helices of the flat ribbon are preferably in selected spaced relation. The wire 715, with the filament glass wound thereon, is wound onto the mandrel 703, preferably under tension, so as to place the adjacent windings of the coil in tight intimate contact. It will be realized that the space between adjacent conductors in a wound coil is at least twice the thickness of the flat ribbon and also the ribbon on adjacent conductors are in crisscross relation at a relatively sharp angle to one another. This latter feature ensures substantially uniform spacing of all the conductors. When the coil has been wound to an endless or closed loop with an appropriate number of turns of conductor, the coil indicated generally by reference numeral 31, is placed on a further mandrel and a ribbon of steel is spirally wound around selected legs thereof to provide the cores 32. A diagrammatic illustration of the same is seen in FIG. 21. The method of winding the ribbon material spirally on the legs is well known as exemplified by the aforementioned Canadian Pat. No 387,222.

To form an encapsulated coil, the wound coil, consisting of a plurality of turns of conductor, may be placed in a suitable mold in an evacuated chamber. Referring to FIG. 22, there is illustrated a mold 1100 having respective inlet and outlet conduits 1101 and 1102 connected thereto and located in the vacuum chamber ofa vessel 1200. The vacuum chamber 1200 may be evacuated by a suitable mechanism 1300 well known in the art. The inlet conduit 1101 extends through the walls of the vacuum chamber 1200 and is connected to a suitable supply of potting compound 70. The potting compound is preferably an epoxy resin selected, dependent upon temperature of operation of the coil in question. The resin, however, as previously mentioned, may be an epoxy, polyester or silicone type. The outlet conduit 1102, which is a bleedoif for the chamber in vessel 1100, also extends through the walls of the vacuum chamber 1200. A valve 1103 located in the bleedoff line may be suitably controlled so as to permit filling of the chamber 1100 with the potting compound 70. The potting compound is then cured and in the case of a thermal setting resin, this may be accomplished by energizing the coil sufficiently to apply appropriate heat. The potting compound fills the space between the adjacent wires provided by the spacer elements (glass material 710) and such potting compound electrically insulates one conductor from another. Accordingly, glass spirally wound on the conductor is for the purpose of maintaining sufficient space between adjacent conductors to allow the encapsulant to flow therebetween. In this regard, the spacer is wound spirally about the conductor as is described above and because of this the strands on one conductor cross, at a relatively sharp angle, the strands on an adjacent conductor. This crisscrossing of the spacer elements ensures substantially uniform spacing of all conductors in the coil.

The core material may be applied to the encapsulated coil (in the dame manner as previously described) and the core and coil assembly then placed in the casing. If desired, the remaining space between the casing and the core and coil assembly may be filled with a potting compound which is the same or different than the encapsulant.

In an alternative procedure, a coil may be wound with spacers thereon as described above with reference to FIG. 20, and core material place on the formed coil. The core and coil assembly may then be placed in the chamber of the casing (50 or 50A) which serves as a mold to encapsulate the core and coil assembly and simultaneously therewith insulates the adjacent conductors one from the other in the coil. A transformer of the foregoing type is dry and because the core and coil is encapsulated, there is no corona discharge or formation of ozone, thus providing for a longer life of the transformer than is the case with a normal air or fluid-cooled transformer.

We claim:

l. A transformer comprising in combination a'core and coil assembly and a casing disposed in complete surrounding rela tion with respect to said core and coil assembly, said casing conforming substantially in shape to said core and coil assembly and thereby providing means for dissipating heat from the transformer, further means for dissipating heat comprising a plurality of heat-conductive fins engaging each of said core and coil assembly and the casing at selected locations and being disposed in a position so as not to intersect the paths of high-intensity flux during operation of the transformer, said heat-conductive strips extending inwardly of the transformer assembly and terminating at a position intermediate the highand low-voltage coils and including further portions extending inwardly of the magnetic core, said magnetic core comprising, in combination, an inner cylinder and an outer cylinder, each consisting of a spirally wound ribbon of magnetizable material disposed about a common axis and wherein the flat faces of the ribbon of the innermost and outermost cylinders are disposed respectively substantially transverse and parallel to said common axis, said innermost cylinder having a plurality of undulations in the ribbon angularly disposed with respect to the length of such ribbon and being of a grain-oriented material with the orientation extending in a direction substantially parallel to the length of such ribbon.

' 2. A transformer as defined in claim 1 including a potting compound encapsulating the core and coil assembly and filling substantially the entire space between the casing and the core and coil assembly thereby to provide a substantially solid, dry transformer.

3. A core of magnetizable material for an inductive device comprising in combination an inner layer and an outer layer each consisting of a ribbon of magnetizable material disposed 1 about a common axis, the surfaces of the ribbon of the innermost and outermost layers being disposed, respectively, substantially transverse and parallel to the said common axis, the ribbon of the innermost layer being undulated angularly to the ler?th thereof.

. A core as defined in claim 3 wherein said undulations exare defined by relatively sharp transitions at each of the valleys and crests thereof.

7. An inductive device comprising at least two electrical coils and a magnetic circuit, said magnetic circuit comprising spirally wound magnetizable material circumscribing a selected portion of said coils and a relatively narrow strip of magnetizable material disposed in edgewise relation intermediate said coils and said spirally wound magnetizable material, said narrow strip comprising ribbon material undulated at an angle to the length thereof and consisting of grainoriented material having the grain orientation extending in a direction substantially parallel to the length of said strip.

8. A transformer comprising a pair of annular coil elements substantially completely circumscribed by a core of magnetizable material, said core comprising a ribbon helically wound about said coil elements, said ribbon being directed in edgewise relation outwardly from such coil elements and havinga plurality of undulations angularly disposed with respect to the length thereof and defined by relatively sharp transition at each of the valleys and crests thereof.

9. Transformer apparatus comprising a. a coil and core assembly including at least a pair of closed loop electrical coils with their respective closed loop surfaces in contiguous side-by-side relationship, and a relatively narrow strip of magnetizable material interposed between the electrical coils and a main body of magnetizable material, such narrow strip being helically wound in circumscribing relationship to a leg portion of the electrical coils defining a cylindrical body in which the narrow strip is in transverse relationship to the longitudinal axis of windings of the electrical coils,

b. a casing of heat-conductive material disposed in surrounding relationship with and conforming substantially to the shape of the coil and core assembly to provide a relatively large mass of heat-conductive material for dissipating heat from such assembly, and

. at least one heat-conductive metal strip located between the electrical coils and extending outwardly therefrom into thermal contact with the casing.

10. Transformer apparatus as defined in claim 9 wherein the magnetizable material is grain-oriented with the grain extending in the direction of the length of such strip.

1 l. A core for an inductive device comprising an elongated ribbon of magnetizable material, the ribbon having a longitudinal axis and a plurality of undulations angularly disposed in transverse relationship with respect to such longitudinal axis, the elongated ribbon being helically wound on edge about a selectedelectrical coil axis such that surfaces of the elongated ribbon defined by such undulations lie in planes which are transverse to the selected axis.

12. The core of claim 11 in which the magnetizable material comprises grain-oriented material with the grain orientation extending in the direction of the longitudinal length of such elongated ribbon.

# i l i i 

1. A transformer comprising in combination a core and coil assembly and a casing disposed in complete surrounding relation with respect to said core and coil assembly, said casing conforming substantially in shape to said core and coil assembly and thereby providing means for dissipating heat from the transformer, further means for dissipating heat comprising a plurality of heat-conductive fins engaging each of said core and coil assembly and the casing at selected locations and being disposed in a position so as not to intersect the paths of highintensity flux during operation of the transformer, said heatconductive strips extending inwardly of the transformer assembly and terminating at a position intermediate the high- and lowvoltage coils and including further portions extending inwardly of the magnetic core, said magnetic core comprising, in combination, an inner cylinder and an outer cylinder, each consisting of a spirally wound ribbon of magnetizable material disposed about a common axis and wherein the flat faces of the ribbon of the innermost and outermost cylinders are disposed respectively substantially transverse and parallel to said common axis, said innermost cylinder having a plurality of undulations in the ribbon angularly disposed with respect to the length of such ribbon and being of a grain-oriented material with the orientation extending in a direction substantially parallel to the length of such ribbon.
 2. A transformer as defined in claim 1 including a potting compound encapsulating the core and coil assembly and filling substantially the entire space between the casing and the core and coil assembly thereby to provide a substantially solid, dry transformer.
 3. A core of magnetizable material for an inductive device comprising in combination an inner layer and an outer layer each consisting of a ribbon of magnetizable material disposed about a common axis, the surfaces of the ribbon of the innermost and outermost layers being disposed, respectively, substantially transverse and parallel to the said common axis, the ribbon of the innermost layer being undulated angularly to the length thereof.
 4. A core as defined in claim 3 wherein said undulations extend in a direction substantially radially outwardly with respect to said common axis.
 5. An article as defined in claim 3 wherein said undulations are substantially uniform along the length of said ribbon and wherein the undulations in adjacent helices are in internested relationship.
 6. An article as defined in claim 5 wherein the undulations are defined by relatively sharp transitions at each of the valleys and crests thereof.
 7. An inductive device comprising at least two electrical coils and a magnetic circuit, said magnetic circuit comprising spirally wound magnetizable material circumscribing a selected portion of said coils and a relatively narrow strip of magnetizable material disposed in edgewise relation intermediate said coils and said spirally wound magnetizable material, said narrow strip comprising ribbon material undulated at an angle to the length thereof and consisting of grain-oriented material having the grain orientation extending in a direction substantially parallel to the length of said strip.
 8. A transformer comprising a pair of annular coil elements substantially completely circumscribed by a core of magnetizable material, said core comprising a ribbon helically wound about said coil elements, said ribbon being directed in edgewise relation outwardly from such coil elements and having a plurality of undulations angularly disposed with respect to the length thereof and defined by relatively sharp transition at each of the valleys and crests thereof.
 9. Transformer apparatus comprising a. a coil and core assembly including at least a pair of closed loop electrical coils with their respective closed loop surfaces in contiguous side-by-side relationship, and a relatively narrow strip of magnetizable material interposed between the electrical coils and a main body of magnetizable material, such narrow strip being helically wound in circumscribing relationship to a leg portion of the electrical coils defining a cylindrical body in which the narrow strip is in transverse relationship to the longitudinal axis of windings of the electrical coils, b. a casing of heat-conductive material disposed in surrounding relationship with and conforming substantially to the shape of the coil and core assembly to provide a relatively large mass of heat-conductive material for dissipating heat from such assembly, and c. at least one heat-conductive metal strip located between the electrical coils and extending outwardly therefrom into thermal contact with the casing.
 10. Transformer apparatus as defined in claim 9 wherein the magnetizable material is grain-oriented with the grain extending in the direction of the length of such strip.
 11. A core for an inductive device comprising an elongated ribbon of magnetizable material, the ribbon having a longitudinal axis and a plurality of undulations angularly disposed in transverse relationship with respect to such longitudinal axis, the elongated ribbon being helically wound on edge about a selected electrical coil axis such that surfaces of the elongated ribbon defined by such undulations lie in planes which are transverse to the selected axis.
 12. The core of claim 11 in which the magnetizable material comprises grain-oriented material with the grain orientation extending in the direction of the longitudinal length of such elongated ribbon. 